Guest blog: Big brother is watching – Spying on the secret lives of endangered seahorses

Louw_CroppedIt’s time for a new guestblog, this one is by the amazing Louw Claassens. Louw is a South-African marine scientist at the Knysna Basin Project and a member of the IUCN Seahorse specialist group. She studies one of the world’s most endangered seahorses, part of her work involves studying their behaviour, which recently resulted in a very interesting publication (go check it out!). In this guestblog she gives you the most important findings of that paper and shares some fantastic video footage. Enjoy!


A big part of ecological research is based on observations – where do animals occur, what do they eat, what do they do. Some of these questions can be answered by using standard scientific methods e.g. a population survey can tell you where animals occur (although why is a whole other kettle of fish!). The tricky part sets in when you want to find out what an animal is doing. Conventionally, this entails going to the animal in question and watching it (sounds pretty simple, right?!). But it is here where observational effect (the act of observing has an effect on behaviour) and observational bias (researcher bias as to expected behaviour) creeps in.

GoPro

I spy with my little…GoPro? (Photo: Louw Claassens)

One of the 21st century solutions to these observational problems, is using cameras to study animals, and we are now even able to use cameras to study animals under water (thank goodness for relatively cheap action cameras such as GoPro’s!). Most fish research uses cameras to look at fish diversity, abundance, and habitat use – with limited work on actual fish behaviour. One of the reasons for this is probably owing to the highly mobile nature of most fish species.

So, is there a place for action cameras in fish behavioural research?

We focused on seahorses to answer this question. The conventional way to study seahorse behaviour entails getting in the water and watching the seahorse go about its business. Or, getting some seahorses and conducting observational research in the lab. The first method is problematic owing to two reasons: 1) Observer effect (the seahorse might act differently when you are watching it), and 2) seahorses move quite slowly most of the time, so detecting a behavioral pattern is quite difficult. Not even to mention the costs and time involved in doing this. The latter method might make sense, but it is well known that animal behaviour in captivity is rarely authentic.

H. capensis_cropped

A very well camouflaged Knysna seahorse (Hippocampus capensis) (Photo: Louw Claassens)

Our aim was to test the efficacy of using video cameras to study the natural behaviour of a seahorse, and we had the perfect opportunity to do this! During a recent population survey of the endangered Knysna seahorse (Hippocampus capensis) in the Knysna estuary (South Africa) we found a stable population within a residential marina estate. The seahorses were found to use artificial Reno mattresses (wire cages filled with rocks). We had the seahorses, we had a relatively protected area to deploy cameras, and we had a sturdy structure to attach the cameras to.

In the first instance, we wanted to see if seahorse behaviour changed throughout the day e.g. between the morning, midday and afternoon. To add to this, we had an opportunity to see what happens to seahorse behaviour during the busy December holiday season. To do this, we used boat noise as a potential stressor (as occupancy of the residential marina estate increases from ~30 % to 100 % over the holiday period).

Video: Aggressive behaviour in the Knysna seahorse (Hippocampus capensis) – main action starts at 0:45.

But first we had to see if cameras successfully captured seahorse behaviour and if they could be used in behavioural assessments. We conducted a short trial period to test this, and found that 49 % of footage recorded contained seahorses. Using this data, we created an ethogram (a catalogue or table of all the different kinds of behaviour or activity observed in an animal) for H. capensis:

  • Feeding: the seahorse is actively searching for prey animals.
  • Irritation: identified by increased clicking and tail adjustments.
  • Moving from holdfast to holdfast: seahorse moves around without any feeding behaviour in-between.
  • Interaction: interaction behaviour can either be between a male and female as part of courting or between seahorses of the same sex and might entail aggression.
  • Stationary: seahorse remains completely still.

Video: Knysna seahorse (Hippocampus capensis) feeding

The next step was to deploy the cameras throughout the day (morning, midday and afternoon) and across the longer time periods (Pre-holiday, Holiday and Post-Holiday). To assess behaviour we used 10-min video sections as a sample and timed all observed behaviour for a single focal animal during the sample.

We recorded hours of footage, of which 57 hours contained suitable footage of seahorse behaviour. Seahorses spent 82 % of their time feeding and we noted courting behaviour exclusively in the morning. This courting behaviour entailed grasping of the female’s tail by the male in an attempt to position himself face to face with the female, followed by swaying movements. We also found that seahorses were more visible and fed more during the morning. There were no differences between the behaviour of males and females.

Graphic footage! Video of a cormorant catching a seahorse (H. capensis)

We observed quite a few cuttlefish, rays and cormorants, but only noted predation by the latter (check out the video above!). Seahorses were also observed happily living side by side with octopus, although octopus are known to eat seahorses in Australia. We also noted some other curious fish, like our temperate butterfly fish (Chaetodon marleyi) (video below) – can you spot the seahorse?

A cold water butterfly fish (Chaetodon marleyi) checking out Louw’s GoPro setup

When we looked at behavioural changes across the longer-term periods, we noted a decrease in visibility and feeding activity of the focal seahorse, with an increase in irritation behaviour, during the holiday period. No courting behaviour was noted during the holiday period – which is a bit concerning, seeing that this species breeding season is from September to March.  Feeding activity and seahorse visibility increased again during the post-holiday period.

So, what does all this tell us? Action cameras are pretty useful in studying natural behaviour of seahorses. Recorded footage can be watched on fast-forward mode which enables a clear view of the behavioural pattern of the animal (something that is quite difficult to see whilst diving, as these guys move so slowly). For H. capensis, it was the first time that natural behaviour was studied, and we gained some valuable information with regards to feeding and interaction behaviour. In addition, it seems that boat noise has a negative effect on the natural behaviour of this species – an aspect which does need further research (preferably, a controlled experimental approach is needed here, to control the vast number of confounding factors that might have played a role!). The use of cameras in natural seagrass habitat also needs to be tested, as visibility might be problematic in dense vegetation.

In the past, the world of underwater research was exclusively meant for the eyes of the researcher/diver. Now, we are able to bring what we experience to the surface and to the lay person. And perhaps the real power of doing this is to create and instill that love and passion for the underwater world that all divers and water lovers have, in all people. I mean, who cannot fall in love with two seahorses doing their morning courting dance?

The secret sex lives of seahorses: mating dance of the Knysna seahorse

Advertisements

Poll: alternative muck diving terms

voteAfter the recent blog about the history of muck diving I received some interesting suggestions about alternative names to describe the activity. Because this is a democratic blog, it’s time for a poll! Tell me (and the rest of the world) which name you prefer and who knows, it might just catch on!

While less talked about than the term “muck diving”, a few people suggested the world needs a fitting name for muck dive enthusiasts (maniacs?).  In bird watching the most fanatic bird watchers are called “twitchers“. I reckon finding an appropriate term for those divers that love nothing more than finding new critters could be interesting.

I have been offered some suggestions, but feel free to add others. For the sake of inspiration, the name “twitcher” actually stems from the nervous behaviour of a well-known bird watcher in the 50s and 60s. So feel free to make fun of your photograph happy critter-enthousiast dive buddies 😉

Luke_Snoot_Black Hairy

Muck-enthusiast in action (can you see the black hairy frogfish?

On the origin of muck diving

The last 3 years of my life have been dedicated to intensely studying critters and socio-economics related to “muck diving”. While this is a relatively common term in the scuba diving world, the vast majority of people haven’t got a clue what muck diving is. I can’t count the number of times people at conferences, meetings, drinks, etc. have gone: “You study what diving???”. Marine scientists seem to prefer hearing “Cryptobenthic fish assemblages on tropical sublittoral soft sediment habitats” than “Critters in the muck”. Each to its own I guess?

Seahorse_muck

Classic muck diving scene (Photo: Dragos Dumitrescu)

It’s not just scientists who are confused, a lot of divers have questions about muck, or at the very least are curious about how it started and where the name came from, so I decided to dig a bit deeper and find out some interesting facts about the origins of muck diving. If you have never heard of muck diving or just aren’t sure what it is, here is how I defined it in my last paper:

“Scuba diving in soft sediment habitats with limited landscape features, with
the explicit goal to observe or photograph rare, unusual, or cryptic species that are seldom seen on coral reefs.”

Or easier: Diving on sand/mud/rubble to find cool animals you don’t see on normal divesites. The word “muck” means either “Dirt, rubbish, or waste matter” or even worse “Farmyard manure, widely used as fertilizer”. In British English it is also used for “Something regarded as distasteful, unpleasant, or of poor quality”. I would guess that it’s the combination of the first and last meanings that inspired the people who started this type of diving.

Muck diving in its current shape has its origins in Milne Bay, Papua New Guinea. On a site called Dinah’s beach,  where Bob Halstead decided to try to do a dive on the site where their boat (the MV Telita) was anchored. The divers were skeptical at first as the site was mostly sand and did not look very appealing, but after discovering tonnes of creatures they had never seen before they were sold and muck diving was born. From its origins in Papua New Guinea, muck diving caught on and became popular across the world, but no place is as well known for muck diving as Lembeh Strait in Indonesia.

Map Milne Bay

Milne Bay, Papua New Guinea, where it all started

It is clear why Lembeh is famous with muck divers, as it really is a great place to dive and find some of the world’s most amazing critters. But how did muck diving in Lembeh kick off? What many people don’t know, is that Lembeh’s origin-story as the world’s most famous muck dive destination is pretty grim. The first resort in Lembeh (Kungkungan Bay Resort) was built in 1994, but the owners did not build their resort with critters in mind….

Back in those days, Lembeh was one of the best sites in the region to watch the big stuff. The plankton-rich waters of Lembeh Strait attracted scores of manta rays, dolphins, sharks,… Until 1996, when mankind showed just how destructive it could be. In March of that year, foreign fishermen came in and (illegally) installed the “Curtains of death”. These were huge nets, placed across the migratory routes of the large fish near Lembeh Strait. The nets were deadly efficient, during the 11 months they were used they caught:

  • 1424 manta rays
  • 577 pilot whales
  • 18 whales
  • 257 dolphins
  • 326 sharks (including whale sharks)
  • 84 turtles
  • many other animals including turtles and marlins

The original article about the curtains of death can’t be found online, but if you are interested, send me an email and I can send a copy. If you want to know more about destructive fishing in Indonesia, this is an interesting source start with.

Rainbow2

Peaceful Lembeh Strait has a turbulent history

The numbers are staggering, and for the few tourism operators in the area it must have been quite a shock. Until they discovered that Lembeh had much more to offer than just the big stuff. While there are no records of it, the story goes that muck diving in the area only properly got started when people started looking down at the sand instead of up at the manta rays. It makes me wonder what the area would have looked liked otherwise, and if muck diving would exist in the way it does now…

As it is now, muck diving is big, it attracts divers from across the globe and new critter hot spots keep on being discovered far beyond from where it all started. It’s exciting to think about how much more we will discover in the future! For me, one of the changes I would like to see, is the actual term “muck diving”. The name coined by Bob Halstead stuck, but I think most people in the diving (and academic) world agree that it isn’t really the most inviting name. I’d like to hear your suggestions (below in comments) on more suitable names for this type of diving and the divers doing it. If I get enough suggestions, I’ll organise a poll later to see what is preferred by divers around the world!

2_MDeBrauwer_JuvenileFrogfish_MDB

It’s all about finding the small stuff – baby Painted frogfish (Antennarius pictus)

PS: Originally I wanted the full title of this blog to be “On the origin of muck diving by Means of Photographer Selection, or the Preservation of Favoured divesites in the search for Critters”. But the long title might have put off those readers who didn’t immediately get the very nerdy biology pun.